Purification of salt solutions



Oct. 5, v1943.

J. D. RUYs ETAL PURIFICATION OF SALT SOLUTIONS Filed Jam.y 31, 1.941

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Qsasw Inventors'. Jan D. Rugs e z mmm .Km0 LLmH un. W m zK Patented Oct. 5, 1943 v PUBJFICATION F SALT SOLU1IONS Jan D. Ruys, Pittsburg, Russell L. Kittie, Concord,

Frank W. Heath, Pittsburg, and William Dietz, Concord, Calif., assignors to Shell Development Company, San Francisco, corporation of Delaware alif., a

Application January 31, 1941, Serial No. 376,812

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This invention relates to an improved process for reacting sulfuric acid with bases. More particularly, it relates to a process wherein waste sulfuric acid in sludges, such, for example, as are produced in petroleum refining, are reacted with bases to form salts which are useful in industry, as, fertilizers, etc. formed are sodium sulfate, calcium sulfate, ammonium sulfate.

It is customary to dispose of waste sulfuric acids that arise from petroleum refining by converting them to useful salts by reacting with suitable bases. Unfortunately, sometimes the salts so produced have either no commercial value or else their value is seriously depreciated because they cannot be freed from a sticky material which coats the individual salt crystals, reducing their purity and at the same time making them very dilcult to handle because of their Vtendency to cake or exhibit abnormal hygroscopic tendencies and other detrimental properties. This prob-I lem of sticky material has been especially serious since the introduction of the alkylation process in the petroleum industry. The waste from acids used as catalysts in this processis such that itis especially dimcult to produce salts of commercial Some examples of salts so tals made from these acids.

It is an object of this invention to improve they process of neutralizing acid sludges with basic`- substances in such a manner that the salt pro-- duced is free from objectionable quantities of sticky material. 1t is a further object to remove the substances giving rise to sticky material from sulfuric acid renery sludge. It is yet another object to recover this sticky material in a form suitable for further processing into valuable products, and it is a final object to provide a process to remove these objectionable impurities which is economical and which can be readily adapted to existing plants for the production of salts from waste 4acid sludges and bases.

The present invention comprises extracting sticky material from a solution obtained by neutralization of acid sludges by means of nitrogenbases such as petroleum nitrogen bases, quinoline, pyridine, and the like. The nitrogen bases form complexes with the sticky material, which is be ure, which is a flow diagram including the essen tial parts of the invention. For purposes of illustration the process will be described'with reference to the production of ammonium sulfate, free from objectionable quantities of sticky material, manufactured in the process of neutralizing petroleum renery acid sludge with ammonia.

Refinery acid sludge, usually containing amounts of nitrogen bases, is admitted through line I to storage tank 2, thence to reactor 4 through line 3. wherein it is contacted with ammonia admitted to reactor! via line 5. Ammonium sulfate circulating vsolution is also continutously admitted to reactor 4 through line I2. Ad-

ditional water may alsorbe supplied to reactor 4 through line 35, if necessary; in order to prevent over-saturation or over-heating of the salt solution formed therein. The salt solution, including oily and tarry materials separated -as the result of the ammonia-acid sludge reaction, passes into a separator Swherein the two` phases separate, an upper oil phase which includes any nitrogen bases present in the acid sludge introduced in re;

actor '4, vand a lower aqueous ammonium sulfate e solution. The oil layer is withdrawn and maybe further treated to liberate any nitrogen 'bases present, as will be described below, the saltv solul tion being passed through line 1 to` an evapora- 1 tion and ltration unit 8.

In evaporation-and filtration unit 8 a portion n A ofA the salt solution is passed without further e treatment into line II to become the circulating solution, the remainder being-subjected .to evan-,fv

oration by means of which ammonium sulfate crystals are formed which are then filtered, washed and dried to produce a commercially useful crystalline ammonium sulfate. n

The circulating ammonium sulfate solution isv passed via line II to mixer I3, wherein it is contacted with nitrogen bases admitted through line I 4 from nitrogen base storage tank I5. This mixture with nitrogen bases leaves mixer I3 via line I6 to settler I1 wherein two phases are formed, a lower aqueous salt phase which is returned via line I8to line I2, and an upper phase consisting predominantly of the complex formed by the nitrogen bases and sticky material fornung 'components, which passes via line I9 to' reactor 20, wherein the vcomplex is reacted with ammonia admitted through line 2l. The ammonia displaces the nitrogen bases in reactor 20, which separate into two phases, one of which consists predominantly of the ammonia-sticky material compound (probably ammonium organic sulfate)' whichv passes vthrough line 2,21to storage not shown. while the regenerated nitrogen bases pass from reactor via line 23 to nitrogen base storage tank I5.

The recovered oil containingA nitrogen bases withdrawn from reactor 4 via line 'l is admitted to extractor 24 wherein it is countercurrently contacted with sulfuric acid admitted to extractor 24 via line 25 from storage tank'2l equipped with supply line 21. The nitrogen basesare extracted by the sulfuric acid, forming a raflinate oil phase substantially free from nitrogen bases which passes from extractor 24 through line 28 to storage not shown. A sulfuric acid extract containing the nitrogen bases passes from extractor 24 through line 29 to nitrogen base reactor 2O wherein it is contacted with anhydrous ammonia admltted through line ll. The ammonia displaces the nitrogen bases, forming ammonium sulfate with the sulfuric acid, which passes from reactor 30 to filtration and evaporation unit 8 via lines Although this invention is illustrated withreference to the production of ammonium sulfate, u

it is not limited thereto but may be equally well applied to the production of sodium sulfate, calcium sulfate, etc., from waste acid sludges, with all of its attendant advantages.

The amount of sticky material that can be removed from the circulating-solution per pound of nitrogen bases depends upon the concentration of the sticky material in thefsolution and therefore will obviously vary with the types of sludge utilized. In general, it has been found that for optimum results the amount of nitrogen bases reacted with circulating solution in mixer i3 shouldl be maintained at a Dointvnot less than 10 grams .per liter and preferably in the neighborhood of 50 grams per liter. Under these circumstances equilibrium relationships seem-to be most favorable for optimum removal or sticky material. For example, by this process it is easily possible to reduce the sticky material content of the dry salt to a quantity not greater than 2 grams per kilogram when employed in the continuous process of neutralizing waste sulfuric acid sludge with ammonia, as for example in the processes disclosed in U. S. Patents 2,026,250 and 2,022,813. The salt thus produced is substantially white in color and non-caking. While this process can be readily, applied batchwise. it is preferably carried out in a continuous manner following the general system illustrated in the drawing. When preparing ammonium sulfate from typical sludges it has been found that about 1% by volume of nitrogen bases are sumcient to react with the sticky material present in the circulating solution. Of this quantity of nitrogen bases about 30% remains dissolved in the aqueous ammonium sulfate solution formed but 1t can be readily recovered as shown in the drawing or in a batch process. In the continuousprocess it has been found satisfactory to divert about 25% of the circulating solution for treatment '(using about 4% by volume of nitrogen. bases in 'I'he amount of nitrogen bases required 'dor a 75 `given sludge being a function of the sticky material content of the sludge as-well as its nitrogen base content, other things being equal it follows that a sludge containing a larger quantity of nitrogen bases requires a smaller auxiliary amount of nitrogen bases for treatment.

While it is possible touse pure nitrogen bases such as pyridine or quinoline, it is preferable to employ petroleum or coal tar nitrogen bases because of their ready availability and low cost. Nitrogen bases such as are obtained in the extraction process disclosed in U. S. Patent 1,411,237, for example, will be found satisfactory for use in the process described above.

We claim as our invention:

l. The continuous process wherein acid sludge derived from the acid treatment of petroleum hydrocarbons is contacted in a reaction zone with a base having a cation selected from the group ccnsisting of potassium, sodium, calcium and ammonia, said acid sludge being characterized by the presence of organic contaminants normally forming a sticky coating on the reaction product of said acid sludge and said base, to form an aqueous sulfate solution containing at least a portion of said organic contaminants and an oil phase, including the steps comprising separating said oil phase and said aqueous sulfate solution in a separating zone, recirculating said aqueous sulfate solution to said reaction zone, continuously withdrawing a portion of said recirculating solution from the recirculating system, reacting a portion of the remainder of said recirculating solution in a reaction zone with a nitrogen base to produce a purified aqueous sulfate solution substantially free from sticky material producing compounds and a nitrogen base-organic contaminant complex, separating said purified aqueous sulfate solution from said nitrogen base containing complex and returning said puriiied aqueous sulfate solution to the recirculation system, reacting said nitrogen base-organic contaminant complex with ammonia in a reaction zone to form a nitrogen base substantially free of organic contaminants and an'ammonia-.organic contaminant compound, separating said nitrogen base and said ammonia-organic contaminant compound and thereafter returning said recovered nitrogen base to said penultimately mentioned reaction zone.

im- 2. In a continuous process wherein acid sludge derived from the acid treatment of petroleum hydrocarbonsis reacted with a base having a cation selected from the group consisting of potassium, sodium, calcium and ammonia, said acid sludge being characterized by the presence of organic contaminants normally7 forming a sticky coating on the reaction product of said acid sludge and said base, to form an aqueous sulfate solution containing a portion oi said organic contaminant, the steps comprising reacting atleast a portion of said aqueous sulfate solution with an organic nitrogen base in a reaction zone to produce an--organic complex containing said sticky vmaterial producing contaminants and a purified aqueous sulfate solution substantially free from sticky material producing compounds, separating said complex from the purified-solution, adding ammonia to theseparated complex whereby nitrogen bases` are liberated, separating and recovering the liberated nitrogen bases and returning them to said reaction zone.

JAN D. RUYS.

RUSSELL L. KI'I'I'LE. FRANK W. HEATH.

WIILIAH H. DIETZ. 

